Fix parsing empty step as input

utils/parset_concat.py

@@ -32,7 +32,7 @@ def concatenate(parsetfile, step_name, step_type, args):
           for line in f_stream.read().splitlines():
               if line.startswith("steps="):
                   _, steps = line.split("=")
-                  steps = [step for step in steps.strip().lstrip("[").rstrip("]").split(",")]
+                  steps = [step for step in steps.strip().lstrip("[").rstrip("]").split(",") if step]
               else:
                   print(line)